WARNING: The following contains spoilers for Solo Leveling Chapter 166 by Chugong, Dubu and h-goon, available in English now on Tapas.
Jinwoo became the family's breadwinner in Solo Leveling when his father disappeared during a raid, leaving him, his sister and mother alone. Soon after, it became just the siblings after their mother fell into an eternal sleep, so Jinwoo had to find some way to earn money and get the medicine she needed. After years of no contact, Jinwoo had pretty much accepted that his father wouldn't be coming back. However, Sung Il-Hwan was still very much alive and had not forgotten his family.
Sung Il-Hwan made his big reappearance in Chapter 56 of Solo Leveling when he emerged out of an A-Rank Dungeon looking more beast than human. One of the first words he spoke was of his desire to return home, where his family awaited. Somehow, even though his devotion to his family was clear, his reunion with Jinwoo in Chapter 166 doesn't strike a very strong emotional note.
When Jinwoo was stabbed by the Frost Monarch, he 'died' and was briefly transported into an alternate reality. The other remaining Monarchs seized the chance to kill him off for good -- except they were thwarted by someone they never expected: a vessel of a Ruler, Jinwoo's father. While Jinwoo was incapacitated, Sung Il-Hwan fought off the two Monarchs by himself, buying enough time for Jinwoo to awaken as the Shadow Monarch. He didn't escape unscathed, however -- blood dripping down from his cut-off arm, Jinwoo's father limped away to wait for his death.
Father and son eventually reunite, and Sung Il-Hwan explains where he's been all these years. After failing to defeat the dungeon boss, he was trapped in a dimensional rift. Desperate to return home to see his family, he made a deal with the Rulers. He would become one of their vessels and carry out their mission to defeat all the Monarchs, including the next Shadow Monarch. Jinwoo's father was anguished to discover he might have to kill his own son and, although he didn't actually attempt this, he didn't actively try to find a way out of it either.
The only reason he wasn't forced to make that choice was because the Rulers decided that keeping Jinwoo alive would be in their favor -- and Il-Hwan's task was now to protect his son. That's not to say he would've gone through with it if the Rulers didn't change their minds, but the fact that he hesitated and was visibly conflicted is a little disconcerting -- especially when he claims he only helped Jinwoo when he saw his son was going to aid the humans. Would Il-Hwan's choice have been different if Jinwoo decided to side with the Monarchs instead?
Their conversation is meant to be heartfelt, with Jinwoo confessing resentment toward his father for not coming back to their family. The problem is that Solo Leveling has focused very little on who his father is until this chapter. Il-Hwan's regret is palpable but when he finally hugs his son as golden cracks appear across his body, it feels melodramatic. On the contrary, when Jinwoo's mother says that she feels they can now move out of the house, it's much more moving because it was established early on that she only stayed because she hoped Il-Hwan would come back.
Despite how short-lived the reunion was, it highlighted some significant similarities between Jinwoo and Il-Hwan. It's remarkable how easily they've accepted both of their respective roles as the Shadow Monarch and vessel of the Ruler -- and the responsibilities associated with them. Both choose to fight alone, with Jinwoo doing so because he doesn't want anyone else in the line of fire. From the very beginning of Solo Leveling, it's been clear that Jinwoo will go to any lengths to protect his family, and his love for them is paralleled by Il-Hwan's choice to sacrifice himself to save his son.